Pharmaceutical compositions for freeze drying

ABSTRACT

A pharmaceutical composition comprising a nucleotide analogue, mannitol and a modifying additive which is sodium chloride or a polyol which is suitable for freeze drying.

The present invention provides a pharmaceutical composition suitable for freeze-drying and a process for the preparation of the composition.

BACKGROUND OF THE INVENTION

Freeze drying is a well known process used to prepare storage stable formulations of pharmaceutical compounds which otherwise suffer degradation when stored in the presence of water, for example, because of disproportionation and/or hydrolysis. A typical freeze drying cycle consists of four stages. Freezing the composition of the compound to be freeze dried, a primary drying cycle which comprises applying a vacuum and sufficient heat to sublimate the ice present in the composition, a second drying cycle which removes any residual water and then recovery of the freeze dried composition. It is an expensive process because it takes a long time and because a low temperature and a vacuum are required. A low temperature is required because the vacuum needs to be applied at a temperature below the eutectic temperature for mixtures of crystalline substances or below the glass transition or collapse temperature for amorphous mixtures. This is to ensure that the water present is vapourised without passing through the liquid state and so that the amorphous mixtures do not collapse. A collapsed amorphous mixture is effectively useless because it is very difficult to reconstitute and may be unstable.

To keep costs down it is preferable for the collapse or eutectic temperature not to be too low in order that the cooling cost is reduced. A higher collapse or eutectic temperature is also advantageous because the evaporation is hastened which reduces the length of time the vacuum is needed. Compositions suitable for freeze drying have been sought which produce a stable product and for which the collapse or eutectic temperature is not too low.

DESCRIPTION OF THE INVENTION

According to a first aspect of the invention there is provided a pharmaceutical composition comprising a nucleotide analogue, mannitol and a modifying additive which is sodium chloride or a polyol.

The invention further provides a pharmaceutical composition in freeze dried, spray dried or vacuum dried form and in reconstituted form.

According to the invention there is further provided a process for the preparation of a composition according to the invention which comprises mixing the ingredients of the composition, and either freezing them and drying the frozen mixture, or spraying them (for example into warm air).

The use of the combination of mannitol and the modifying additive in the compositions of the invention has unexpectedly been found to improve the compositions long term stability after freeze drying. Another advantage of using such a combination is that vial breakage or cracking during freeze-drying is prevented.

A nucleotide is a compound comprising a purine or pyrimidine base attached to a pentosugar wherein one or more of the hydroxy groups of the pentosugar are phosphorylated by a mono- or polyphosphate. A nucleotide analogue for use in the invention is in general a compound in which one or more of the three moieties of which a nucleotide is comprised is modified, for example, by attachment of one or more substituents and/or by replacement of one or more of the skeletal atoms.

The nucleotide used in the invention is preferably a nucleotide from WO 94/18216 , that is to say a compound of formula (I): ##STR1## wherein R¹ and R² independently represent hydrogen or halogen, R³ and R⁴ independently represent phenyl, or C₁₋₆ -alkyl optionally substituted by one or more substituents selected from OR⁵, C₁₋₆ -alkylthio, NR⁶ R⁷, phenyl, COOR⁸ and halogen, R⁵, R⁶, R⁷ and R⁸ independently represent hydrogen or C₁₋₆ -alkyl, and X represents an acidic moiety, or a pharmaceutically acceptable salt thereof.

Compounds of formula (I) may exist in tautomeric, enantiomeric and diastereomeric forms, all of which are included within the scope of the definition.

Pharmaceutically acceptable salts of the compounds of formula (I) include alkali metal salts, e.g. sodium and potassium salts; alkaline earth metal salts, e.g. calcium and magnesium salts; salts of the Group III elements, e.g. aluminium salts; and ammonium salts. Salts with suitable organic bases, for example, salts with hydroxylamine; lower alkylamines, e.g. methylamine or ethylamine; with substituted lower alkylamines, e.g. hydroxysubstituted alkylamines; or with monocyclic nitrogen heterocyclic compounds, e.g. piperidine or morpholine; and salts with amino acids, e.g. with arginine, lysine etc., or an N-alkyl derivative thereof; or with an aminosugar, e.g. N-methyl-D-glucamine or glucosamine. The non-toxic physiologically acceptable salts are preferred, although other salts are also useful, e.g. in isolating or purifying the product.

Alkyl groups in the definitions of compounds of formula (I) include straight, branched or cyclic, saturated or unsaturated alkyl groups. Aryl groups in the definitions of compounds of formula (I) include both carbocyclic and heterocyclic groups. The groups may contain rings or various numbers of C-atoms and may be fused ring structures. Particular carbocyclic aryl groups which may be mentioned are phenyl and naphthyl. Heteroaryl groups include nitrogen, oxygen or sulphur heterocycles and may contain one or more heteroatoms. Examples of heterocycles containing only one heteroatom include pyrrole, furan, thiophen and pyridine. Groups containing more than one heteroatom include pyrazole, oxazole, thiazole, triazole, oxadiazole, thiadiazole etc.

Halogens which R¹ and R² may represent include F, Cl, Br and I. Preferably R¹ and R² are the same and more preferably represent Cl.

Preferably R³ and R⁴ represent C₁₋₆ -alkyl optionally substituted by one or more substituents selected from OR⁵, C₁₋₆ -alkylthio, NR⁶ R⁷, phenyl, COOR⁸ and halogen. Halogens with which R³ and R⁴ may be substituted include Cl, Br and I, and especially F.

Particularly preferred are compounds in which R³ represents C₁₋₆ -alkyl optionally substituted by C₁₋₆ -alkylthio. Particular alkyl groups that R³ may represent include propyl and butyl, and especially ethyl. Particular substituted alkyl groups that R³ may represent include 2-(methylthio)ethyl.

Preferably R⁴ represents C₁₋₆ -alkyl optionally substituted by one or more, e.g. three, halogen atoms. Particular groups that R⁴ may represent include propyl and 3,3,3-trifluoropropyl.

Acidic moieties which X may represent include Bronsted-Lowry acids, i.e. moieties which act as proton donors. The acidic moiety may be mono- or poly-acidic. Specific acidic moieties which may be mentioned include --P(O)(OH)₂, --SO₃ H and --CO₂ H. Preferably X represents --P(O)(OH)₂.

Most preferably, the nucleotide analogue is N-[2-(methylthio)ethyl]-2-[(3,3,3-trifluoropropyl)thio]-5'-adenylic acid, monoanhydride with dichloromethylenebisphosphonic acid or a pharmaceutically acceptable salt thereof, that is to say a compound of formula (Ia): ##STR2##

Most preferably the compounds of formula (Ia) is in the form of the tetrasodium salt.

Compounds of formula (I) may be prepared using the methods disclosed in WO 94/18216. The compounds of formula (I) are useful because they exhibit pharmacological activity in mammals. In a further aspect the invention provides a composition as defined herein for use in therapy, in particular, in the prevention of platelet aggregation. The compositions of the invention therefore act as anti-thrombotic agents.

In a further aspect the invention provides a method of treating a platelet aggregation disorder which method comprises treating a subject suffering from a said disorder with a therapeutically effective amount of a pharmaceutical composition as defined herein.

In a still further aspect the invention provides use of a pharmaceutical composition as defined herein in the manufacture of a medicament for treating a platelet aggregation disorder.

The modifying additive or agent is preferably a suitable polyol. This is because when NaCl is used as the modifying agent, the profile of impurities is unfavourable.

A polyol suitable for use in the invention is in general a straight chain polyhydric alcohol or a cyclic molecule comprising one or more keto or aldehyde groups which is preferably a carbohydrate. The polyol used in the composition according to the invention is preferably sorbitol, lactose, sucrose, inositol or trehalose. More preferably the modifying agent is sorbitol because it has surprisingly been found that the long term stability of freeze dried compositions comprising sorbitol is improved compared to such compositions containing other modifying agents.

The composition according to the invention preferably comprises mannitol as a crystallising agent. Suitably the compositions of the invention comprise about 1% or more by weight of mannitol, for example 20-40%. However there is a problem with mannitol in that on freeze drying, the vials containing the mixture without the modifying additive tend to crack due to an amorphous to crystalline phase transition. The amount of the modifying additive is preferably sufficient to prevent this phase transition from occurring, for example about 3 to 25%. A suitable amount can easily be determined by conventional analytical techniques such as differential scanning calorimetry. However the amount of the modifying agent should not be so much as to cause collapse of the composition.

The water content of the formulation is preferably less than 5% by weight, more preferably less than 2% by weight and most preferably less than 1% by weight.

The pharmaceutical composition according to the present invention optionally additionally comprises a pharmaceutically acceptable excipient, for example a chelating or sequestering agent, an antioxidant, a tonicity adjusting agent, a pH modifying agent and/or a buffering agent, for example one or more of those disclosed in "Review of Excipients and pH's for Parenteral Products used in the United States" Yu-Chang John Wang and R R Kowal, J Parenteral Drug Association, 34, 452-462 (1980).

The process for preparing the pharmaceutical composition according to the present invention is suitably carried out using any lyophilisation, vacuum drying or spray drying technique commonly used within the pharmaceutical area. In a further aspect the invention provides a process for preparing a pharmaceutical composition as defined herein which comprises mixing a nucleotide analogue, mannitol and a sodium chloride or polyol modifying additive and subjecting the mixture to a lyophilisation, vacuum drying or spray drying procedure.

A preferred process according to the invention is a vial freeze-drying process. Such a process comprises filling sterile vials with a sterile filtered solution of the composition according to the invention. A sterile freeze-drying stopper is partially inserted into the vial which is frozen, e.g. at a temperature from -30 to 40° C., and thereafter vacuum dried in the frozen state. After drying the stopper is fully inserted before removing the vial from the lyophilization unit.

Upon use but before administration, the pharmaceutical compositions according to the present invention are generally reconstituted in a pharmaceutically acceptable diluent. Examples of pharmaceutically acceptable diluents include water, saline and dextrose. Preferably water is used as the diluent. In a further aspect the invention provides a process for preparing a pharmaceutical composition as defined herein which comprises mixing a nucleotide analogue, mannitol and a sodium chloride or polyol modifying additive with a pharmaceutically acceptable diluent.

Suitably a solution of the pharmaceutical composition according to the invention obtained after reconstitution and containing mannitol is an isotonic solution.

In a preferred embodiment the pH of the composition of the present invention is from about 6 to about 10, more preferably from about 7 to about 9.

The pharmaceutical composition according to the present invention when reconstituted is preferably administered by injection intravenously, subcutaneously or intramuscularly, preferably intravenously.

The compositions according to the invention may be packed in suitably adapted pharmaceutical application devices, for example syringes, vials or ampoules, such that the addition of water allows the in situ preparation of an aqueous solution of the active ingredient in a form suitable for immediate adminstration to the patient. Such devices form a further aspect of the invention.

EXAMPLES

The invention will now be described in more detail by the following examples.

Example 1

The freeze dried compositions listed in Table 1 were prepared as follows. For each batch 5 ml aliquots of the solution shown were filled into vials and then placed in a Secfroid Lyolab G freeze drier. They were frozen to -35° C., subjected to 2 hours primary drying at -30° C., followed by 33 hours of primary drying during which the temperature was ramped to 35° C. and then 12 hours secondary drying at 35° C. The vacuum was held at 100 mTorr throughout primary and secondary drying.

                  TABLE 1                                                          ______________________________________                                                         Amount/                 Amount/                                Batch Component % by wt   Batch                                                                               Component                                                                               % by wt                                ______________________________________                                         1     Analogue  2.2       2    Analogue 2.4                                          Sorbitol  21.1           NaCl     1.4                                          Mannitol  76.6           Mannitol 96.2                                   ______________________________________                                    

wherein the analogue is compound of formula (Ia). They were then stored under the conditions shown in Table 2 and suffered the degradation shown by the amount of impurities.

                  TABLE 2                                                          ______________________________________                                         Batch   Storage conditions                                                                           Storage time                                                                             Total Impurities                               ______________________________________                                         1       -20° C./ambient                                                                       12        1.23                                                   humidity      26        1.26                                           1       4° C./ambient                                                                         4         1.51                                                   humidity      8         1.63                                                                 12        1.34                                                                 26        1.36                                           1       25° C./60% RH                                                                         4         1.57                                                                 8         1.75                                                                 12        1.51                                                                 26        1.55                                           1       40° C./75% RH                                                                         4         1.95                                                                 8         2.22                                                                 12        2.44                                           2       -20° C./ambient                                                                       12        1.56                                                   humidity      26        1.50                                           2       4° C./ambient                                                                         4         1.40                                                   humidity      8         1.57                                                                 12        1.54                                                                 26        1.47                                           2       25° C./60% RH                                                                         4         1.44                                                                 8         1.55                                                                 12        1.61                                                                 26        1.67                                           2       40° C./75% RH                                                                         4         1.80                                                                 8         2.10                                                                 12        1.95                                           ______________________________________                                    

wherein the amount of impurities is a percentage by weight and RH means relative humidity.

Example 2

The freeze dried compositions listed in Table 3 were prepared as follows. For each batch 3 ml aliquots of the solution shown were filled into vials and then placed in a Virtis Genesis 25EL freeze drier. They were frozen to -35° C., subjected to 2 hours primary drying at -30° C., followed by 25-28 hours of primary drying at 5° C. and then 11 hours secondary drying at 35° C. The vacuum was held at 100 mTorr throughout primary and secondary drying.

                  TABLE 3                                                          ______________________________________                                                         Amount/                 Amount/                                Batch Component % by wt   Batch                                                                               Component                                                                               % by wt                                ______________________________________                                         3     Analogue  21        8    Analogue 38.3                                         Sorbitol  19.8           Sorbitol 12                                           Mannitol  59.2           Mannitol 49.7                                   4     Analogue  20.9      9    Analogue 37.1                                         Inositol  20.4           Sucrose  6.1                                          Mannitol  58.7           Mannitol 56.8                                   5     Analogue  18.8      10   Analogue 35.1                                         Sucrose   22.6           Sorbitol 18.1                                         Mannitol  58.6           Mannitol 46.8                                   6     Analogue  18.8      11   Analogue 48.2                                         Trehalose 22.6           Sorbitol 16.6                                         Mannitol  58.6           Mannitol 35.2                                   7     Analogue  38.3      12   Analogue 58.9                                         Sorbitol  3              Sorbitol 15.2                                         Mannitol  58.7           Mannitol 25.9                                   ______________________________________                                    

wherein the analogue is a compound of formula (Ia).

Each batch was then stored at 40° C. and 75% relative humidity and suffered the degradation shown in Table 4.

                  TABLE 4                                                          ______________________________________                                               Storage time                                                             Batch (weeks)   Impurity A                                                                               Impurity B                                                                             Total Impurities                             ______________________________________                                         3     0         <0.05     0.06    0.63                                               4         0.06      0.06    0.77                                               12        0.08      0.07    0.75                                               26        0.12      0.08    0.76                                         4     0         <0.05     0.07    0.63                                               4         0.07      0.09    0.83                                               12        0.24      0.32    1.17                                               26        0.17      0.08    0.90                                         5     0         0.07      0.07    0.74                                               4         0.10      0.08    0.86                                               12        0.14      0.07    0.82                                               26        0.24      0.08    0.99                                         6     0         <0.05     0.06    0.69                                               4         0.14      0.08    1.00                                               12        0.26      0.08    0.96                                               26        0.46      0.10    1.15                                         7     0         0.06      0.11    0.81                                               4         0.16      0.16    0.89                                               12        0.29      0.22    1.10                                         8     0         <0.05     0.09    0.68                                               4         0.08      0.09    0.73                                               12        0.12      0.11    0.83                                         9     0         0.05      0.10    0.74                                               4         0.18      0.16    0.89                                               12        0.30      0.18    1.02                                         10    0         <0.05     0.06    0.32                                               4         0.05      0.07    0.39                                               12        0.08      0.07    0.43                                         11    0         <0.05     0.06    0.32                                               4         0.05      0.06    0.38                                               12        0.08      0.07    0.48                                         12    0         <0.05     0.06    0.33                                               4         <0.05     0.07    0.33                                               12        0.05      0.06    0.38                                         ______________________________________                                    

wherein the amount of each impurity is a % by weight and impurity A is a compound of formula (Ib) which is ##STR3## and impurity B is a compound of formula (Ic) ##STR4## wherein Q represents ##STR5## 

What is claimed is:
 1. A pharmaceutical composition comprising a nucleotide analog, mannitol and a modifying additive which is sodium chloride or a polyol, wherein the nucleotide is a compound of formula wherein R¹ and R² independently represent hydrogen or halogen, R³ and R⁴ independently represent phenyl, or C₁₋₆ -alkyl optionally substituted by one or more substituents selected from OR⁵, C₁₋₆ -alkylthio, NR⁶ R⁷, phenyl, COOR⁸ and halogen,R⁵, R⁶, R⁷ and R⁸ independently represent hydrogen or C₁₋₆ -alkyl, and X represents an acidic moiety, or a pharmaceutically acceptable salt thereof.
 2. A pharmaceutical composition according to claim 1 in which R¹ and R² are halogen, R³ is C₁₋₆ -alkyl optionally substituted by C₁₋₆ -alkylthio, R⁴ is C₁₋₆ -alkyl optionally substituted by halogen, and X is --P(O)(OH)₂, --SO₃ H or --CO₂ H.
 3. A pharmaceutical composition according to claim 1 wherein the nucleotide is N-[2-(methylthio)ethyl]-2-[(3,3,3-trifluoropropyl)thio]-5'-adenylic acid, monoanhydride with dichloromethylenebisphosphonic acid.
 4. A pharmaceutical composition according to claim 1 in which the modifying additive is a polyol.
 5. A pharmaceutical composition according to claim 1 in which the modifying additive is sorbitol.
 6. A pharmaceutical composition according to claim 1 which further comprises 1% or more by weight of manntiol.
 7. A pharmaceutical composition according to claim 1 which is in freeze-dried, spray dried or vacuum dried form.
 8. A pharmaceutical composition according to claim 7 which is in reconstituted form.
 9. A pharmaceutical composition according to claim 1 which is at a pH of about 6 to about
 10. 10. A pharmaceutical composition according to claim 1 in which the water content is less than 5% by weight.
 11. A process for the preparation of a pharmaceutical composition according to claim 7 which process comprises mixing the ingredients of the composition, and either freezing them and drying the frozen mixture, or spraying them.
 12. A method of treating a platelet aggregation disorder which method comprises treating a subject suffering from a said disorder with a therapeutically effective amount of a pharmaceutical composition as defined in claim
 2. 13. A process for preparing a pharmaceutical composition as defined in claim 1 which comprises mixing a nucleotide analogue, mannitol and a sodium chloride or polyol modifying additive and subjecting the mixture to a lyophilisation, vacuum drying or spray drying procedure. 